Ultra-long wavelength Dirac plasmons in graphene capacitors*

Graphene is a recognized 2D platform for plasmonics in the THz and mid-IR domains. These high-energy plasmons couple to the dielectric surface modes, giving rise to hybrid plasmon-polariton excitations. The ultra-long wavelength GHz range addresses the low energy end of the spectrum, where Dirac plasmons are damped by ohmic losses but essentially decoupled from environment. Using hBN encapsulated graphene [1], we demonstrate a plasma resonance capacitor [2] showing a quarter-wave plasmon mode, at 40 GHz, with a quality factor Q=2. The resolution of the resonant technique yields precise determinations of the electronic compressibility, kinetic inductance, and mean free-path, in good agreement with theory. The 100µm-long wavelength allows engineering of doping-modulated devices where plasmons are controlled by Klein tunneling. Downscaling for room temperature operation opens up perspectives in microwave detection for wireless communication and sensing [3].

[1] L. Banszerus et al, Nano Lett. 16, 1387 (2016)
[2] H. Graef et al., J. Phys. Mater. 1, 01LT02 (2018)
[3] D.A. Bandurin et al, arXiv:1807.04703 (2018)